Assessing the presence of biomarkers, such as estrogen receptors (ER), progesterone receptors (PR), human epidermal growth factor 2 (HER2), and determining the proliferative index Ki67 helps defining BC subtypes, each having a different response to endocrine therapy, chemotherapy or HER2 targeted treatment such as trastuzumab [5]. This evidence concerns the gene MKI67 and breast cancer.